I am looking for a tool that could help me compare the contents of 2 big folders and detect what's changed in one of them (files added, modified, moved, copied) compared to the target. I also want to be able to sync the two folders using my preferences (custom sync).

I want to use this as a backup, but it shouldn't be completely automatic (I want to see what is synchronized, what's copied). The reason for this is that I maybe want to keep some files on the target (old archived projects) but delete them from the source (to save up space).

It's very important that it detects moved files/folders in the source directory (so I avoid duplicate if I do one-way synchronize -- I have the habit of reorganizing my directory structure, therefore moving folders and creating subfolders)

It also needs to be fast because I'm talking about large directories (~ 60 000 files)

So far I've tried the following software, but have not found something that could satisfy my backup needs:

  • ViceVersa Pro (it's nice and fast, but it couldn't detect moved files)
  • WinMerge (very slow to compare 60 000 files - can't afford time loss when doing more frequent backups) (update: this tool doesn't detect moved files either!, it's just much slower than ViceVersa)

EDIT: I changed over to Mac so now I need one that works with MacOS (not necessarily for Windows)

  • 1
    Ahh, so you Reorganise the the other location, and need for the utility to just go through all the subfolders make a raw list then compare the files reguardless of the folder arrangement?
    – Psycogeek
    Commented Oct 2, 2011 at 18:46
  • yes that would be nice, instead of deleting, then copying the files again (and that might delete some files that I specifically put only on the backup disk - to save space)
    – Cristian
    Commented Oct 5, 2011 at 9:04
  • It sure would be, and it seems entierly possible. No sync or diff program normally would work that way, because they start more as developer tools, so everything must be same sub folders and all. But there are probably a million users who just want to know if its in both places. A request at sourceforge or developer location? a Duplication finder would provide a list, but it would have to be checked
    – Psycogeek
    Commented Oct 5, 2011 at 9:25

4 Answers 4


Try out Unison. Free/open source. Uses rsync algorithm for sync, so only changed bits move. Handles 2-way sync. Fast.

Unison is a file-synchronization tool for Unix and Windows. It allows two replicas of a collection of files and directories to be stored on different hosts (or different disks on the same host), modified separately, and then brought up to date by propagating the changes in each replica to the other.

  • looks nice, I'll try it and check its speed later :)
    – Cristian
    Commented Oct 10, 2011 at 9:03
  • I like it! The analyzing speed is manageable, for 4.5 GB it took ab. 12 min, but copying is fast enough and I like the list view with the changes, where you can select left or right, just like in a diff tool. The add profile window could use a bit more work. But all in all, a tool that I'd use from time to time to tell me the actual differences between 2 moderately large folders. Thanks!
    – Cristian
    Commented Oct 10, 2011 at 19:27
  • 1
    1 other thing: If one of the endpoints is another system, it can spawn another instance via an SSH tunnel to work in client/server mode similar to an rsync c/s setup. This will greatly speed up checking and syncing, especially if your connection is 100 Mb/s or less (e.g. WiFi, most internet connections, etc.). It can be tricky to set up, especially on Windows hosts, but it's well worth the trouble. Times went down by an order of magnitude when I did that for my laptop's WiFi sync.
    – afrazier
    Commented Oct 10, 2011 at 19:33
  • well I didn't use networks this time. I just synced a folder on my external HDD with my Mac.
    – Cristian
    Commented Oct 11, 2011 at 7:22

Have you look at the free utility SyncToy 2.1 I use it to keep backups to USB drive and it may meet your needs. I hope this helps.

  • thanks, but I think I need one that works with Mac since I changed my computer. Will try this tool on my old computer, when I get home.
    – Cristian
    Commented Oct 5, 2011 at 9:06
  • @Christian you may want to re-tag to include Mac I hope you find what you need.
    – N4TKD
    Commented Oct 5, 2011 at 10:32

A very old trick : for every file, make another file adding the suffix .crc ... with the crc of its pal.

Now, you

  1. make the crc trick for every new incoming file
  2. you just compare the crc files : blazing fast, also over slow network links

Under linux there is the standard utility cksum. Similar tools are wide-spread, from the ancient time of BBS over 9600 baud tel.co. links :-)


I think GoodSync can do this, but the free/trial version has file number limits.

You may want to run rsync in dry-run mode or run diff to compare folders if you want free commandline solutions.

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